The thermal decomposition of smithsonite (ZnCO 3 ) was studied to obtain a universal kinetic description of the process applicable to a range of reaction conditions. A synthesized ZnCO 3 was subjected to thermoanalytical measurements under various heating and atmospheric conditions in a flow of dry N 2 gas, or N 2 −CO 2 or N 2 −H 2 O mixed gases. Systematic shifts of the reaction temperature to higher or lower values by the effects of CO 2 or H 2 O, respectively, were identified as specific characteristics of the system. With reference to the physicogeometrical kinetic behavior of the reaction in a flow of dry N 2 gas, the retardation effect of CO 2 was demonstrated in the scheme of the physicogeometrical consecutive surface reaction (SR) and phase boundary-controlled reaction (PBR). The individual kinetics of SR and PBR were universally described over different CO 2 partial pressures using an accommodation function (AF) obtained by considering the consecutive elementary steps of SR and PBR. The catalytic effect of water vapor was assumed to result from contributions of water molecules to the consecutive elementary steps of SR and to the crystal growth of the solid product of the reaction (ZnO). An alternative AF derived considering the adsorption of water molecules on solid surfaces allowed us to obtain the universal kinetic description of the thermal decomposition over different water vapor pressures.
The bitterness of bitter substances can be measured by the change in the membrane electric potential caused by adsorption (CPA) using a taste sensor (electronic tongue). In this study, we examined the relationship between the CPA value due to an acidic bitter substance and the amount of the bitter substance adsorbed onto lipid/polymer membranes, which contain different lipid contents, used in the taste sensor. We used iso-α-acid which is an acidic bitter substance found in several foods and beverages. The amount of adsorbed iso-α-acid, which was determined by spectroscopy, showed a maximum at the lipid concentration 0.1 wt % of the membrane, and the same phenomenon was observed for the CPA value. At the higher lipid concentration, however, the amount adsorbed decreased and then remained constant, while the CPA value decreased monotonically to zero. This constant adsorption amount was observed when the membrane potential in the reference solution did not change with increasing lipid concentration. The decrease in CPA value in spite of the constant adsorption amount is caused by a decrease in the sensitivity of the membrane as the surface charge density increases. The reason why the peaks appeared in both the CPA value and adsorption amount is based on the contradictory adsorption properties of iso-α-acid. The increasing charged lipid concentration of the membrane causes an increasing electrostatic attractive interaction between iso-α-acid and the membrane, but simultaneously causes a decreasing hydrophobic interaction that results in decreasing adsorption of iso-α-acid, which also has hydrophobic properties, onto the membrane. Estimates of the amount of adsorption suggest that iso-α-acid molecules are adsorbed onto both the surface and interior of the membrane.
Thermal oxidation of carbon/carbon composites in an oxidizing atmosphere is a multistep process regulated by the intrinsic heterogeneity of the solid-gas reaction, the additional heterogeneity of the compositional and structural characteristics of the composite, and how these two properties change as the reaction progresses. By focusing on the overlapping features of the component reaction steps, the kinetic characterization of the multistep kinetic process was studied to reveal the correlation between the thermal oxidation behavior and the compositional and structural characteristics of carbon/carbon composites. Using commercially available mechanical pencil leads as a typical model system for a carbon/carbon composite, the thermal behaviors of two different leads manufactured by different companies were investigated comparatively via thermoanalytical techniques and morphological observations. On the basis of a reaction model considering the different reactivities of the main (graphite) and secondary (carbonized polymer) carbon components, the kinetic features of two partially overlapping reaction steps were revealed via a kinetic deconvolution analysis of the thermoanalytical data for the thermal oxidation process. The kinetic results were correlated with the compositional and structural characteristics of carbon/carbon composites using morphological observations of the partially reacted samples. Herein, the practical usefulness of the kinetic analysis in characterizing carbon/carbon composites is discussed.
The thermal behaviors of carbon/carbon (C/C) composites in flowing air were investigated on the basis of mechanical pencil leads with different hardness values and diameters as a model system. Two separated mass-loss processes were observed during heating the mechanical pencil leads in air, which are attributed to the evaporation–decomposition of an impregnation agent and the subsequent thermal oxidation of the residual C/C composite. The thermal behaviors were invariant among the mechanical pencil leads with different diameters, but they systematically changed with hardness. Variations in the thermal behaviors can be quantified by the mass-loss value during the evaporation–decomposition of the impregnation agent, in addition to the kinetic deconvolution analysis that was applied to the multistep thermal oxidation process of carbon components with different reactivities. These results correlate the thermal behavior with the compositional and structural characteristics of C/C composites, which can be useful for characterization and product control.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.